Mikhail Khodorkovsky has said after his release from prison that he had sought a pardon from Russian President Vladimir Putin for family reasons and did not admit guilt.

In a statement on December 20, Khodorkovsky said, "The issue of admission of guilt was not raised."

Khodorkovsky, a former oligarch and Kremlin critic, was released from prison in the northwestern region of Karelia earlier on December 20 after he was pardoned by President Vladimir Putin on "humanitarian grounds."

Hours after his release, Khodorkovsky arrived at Berlin's Shoenefeld airport, where he was met by former German Foreign Minister Hans-Dietrich Genscher.

Chancellor Angela Merkel said Genscher had played a role "behind the scenes" to secure Khodorkovsky's release.

"I don't want to assess the reasons for it now. At any rate, firstly, it was important not to forget him and to keep drawing attention to the issue, and secondly, there was a window of opportunity that was used," Merkel said. "This is a good message."

Mikhail Khodorkovsky

As the head of Yukos oil and valued at $15 billion, Khodorkovsky was once Russia's richest man. He benefitted from the country's privatization of state assets in the 1990s.

In October 2003 Khodorkovsky was arrested and later convicted of tax evasion. He and his business partner, Platon Lebedev, were sentenced to eight years in prison. Khodorkovsky had refused to heed warnings from President Vladimir Putin that oligarchs were to avoid politics, and his imprisonment was widely viewed as politically motivated.

In 2010, just a year before he was scheduled to be released, Khodorkovsky was convicted and sentenced to a second prison term for money laundering and embezzlement. He is set to be released in August 2014.

Prison officials said in a statement that Khodorkovsky had petitioned to be allowed to leave the country to see his mother, who recently underwent medical treatment in Germany but has since returned to Russia.

Both Khodorkovsky's parents are expected to fly to Germany on December 21.

Khodorkovsky's father, Boris, told reporters that the family felt "joyful" upon hearing of his son's release.

He headed the country's largest oil company when he was arrested in 2003 and charged with tax evasion. He was convicted two years later. In 2010, he was convicted of embezzlement at a second trial.

Supporters say his financial support for opposition parties upset the Kremlin and that his prosecution was politically motivated.

His prison term had been due to expire at the end of August 2014.

Critics say that by Khodorkovsky's release and a wide-ranging amnesty this week, Putin may be trying to ease criticism of Russia's human rights record ahead of the Winter Olympics in Sochi in February 2014.

Russian businessman and opposition politician Mikhail Prokhorov said he was glad that Khodorkovsky was "finally" released.

Prokhorov, who finished third in the 2012 presidential election, said he would "certainly call him" after Khodorkovsky spends some time with his family.

Later on December 20, U.S. Secretary of State John Kerry welcomed Khodorkovsky's release.

A written statement from Kerry noted that Washington has repeatedly expressed concerns about what it described as “due process violations and selective prosecution in Russia, including against Khodorkovsky and his business partner Platon Lebedev, who remains in prison.”